Development and Photographic Techniques
Michael A. Smith, B.A.
George Washington University, Washington, DC
Alexandria Police Department, Alexandria, VA
Latent fingerprint development on latex gloves is possible in many circumstances. The tight-fitting, non-porous nature of the gloves themselves leads to considerable perspiration of the hands. When the gloves are removed, they are typically “peeled” off, preserving the fingerprint evidence on them without smearing. These latent fingerprints can subsequently be developed and photographed, using conventional techniques outlined below. Special photographic techniques can be utilized to enhance the quality of photographs used for comparison with known ten-print cards, elimination prints, other fingerprints recovered from the scene, and entry into an Automated Fingerprint Identification System (AFIS). We must remember as we develop and photograph latent fingerprint evidence what our goal is–the identification or elimination of suspects.
Remember that when removed, these gloves are often turned inside-out. Careful examination, using an oblique light source, can often reveal which side is the interior of the glove. For purposes of development and photography, the gloves should be inside-out, so the surface in contact with the palm and fingers is on the outside. Attention should be paid to the entire surface of the glove: the palm, the back, and both the inside and outside of the cuff. Identifying characteristics can be left on all of these areas. During testing, an excellent thumbprint was discovered on the interior of the cuff, put there when the gloves were pulled on. Development of latent fingerprints on latex gloves can be achieved using standard, non-porous development techniques, however some techniques are more effective than others.
Traditional and Magnetic Powders
Fingerprint powders attach to sweat and oil residues left on the inside of the glove. Some success was achieved using traditional powder, especially when the latent fingerprints were fresh. Magnetic powder, however, was more successful in every instance. Using the magnetic brush to draw the powder across the surfaces of the glove brought out clearer, more readily identifiable prints.
Special fingerprint powders that fluoresce when illuminated by an Alternate Light Source (ALS) or a laser are very effective on their own, and also when combined with cyanoacrylate (superglue) fuming (q.v.). Fluorescent powders are available in a variety of colors, both magnetic and non-magnetic. A drawback to the use of fluorescent powders is that they require special equipment (e.g. an ALS) to visualize and photograph their results. Advantages include the ability to visualize very faint latent fingerprints using small amounts of powder, and the sharpness and vivid contrast achieved photographing the evidence.
Small Particle Reagent
Small particle reagent (SPR) is a wet process used to develop latent fingerprints on smooth, non-porous surfaces (e.g. car exteriors in the rain). Experimenting on latex gloves showed poor results overall. In the laboratory, the fingerprints developed using this method were too faint to photograph. After drying, the fingerprints can be further developed by the application of fingerprint powders (q.v.).
Excellent results can be achieved using cyanoacrylate (superglue) fuming. The latex gloves are placed in a fuming chamber with the chemical, and a build-up of cyanoacrylate esters occurs. Care must be taken to avoid over-development. Fuming can be accelerated by the addition of heat, moisture, and catalyzing agents (e.g. NaOH). The results are visible, white fingerprints. These visible fingerprints can be further treated in a number of ways: fingerprint powders (q.v.) or fluorescent dyes (e.g. Rhodamine). Gloves treated with Rhodamine or fluorescent powders must be examined using an ALS or laser.
Test in the laboratory showed the best results from the application of fluorescent powder. Gloves recently removed (within 2 hours) showed excellent results from powder alone. Gloves removed the previous day benefitted greatly by cyanoacrylate fuming, followed by application of fluorescent powder. The prints developed this way were examined and photographed using an ALS.
Photographing developed fingerprints on latex gloves uses standard techniques for evidence macrophotography. A copy stand is used, and photographs are taken with a scale to make 1:1 reproduction possible. Special filters, goggles, and light sources are needed to visualize fluorescent evidence. Fingerprint comparison photographs are typically black-and-white. ALS/LASER enhanced photographs are negative images; the fluorescent dyes and powders are white and the background is black. Often, these photographs are reversed in the darkroom to make comparison easier for the latent print examiner.
The irregular shape of latex gloves, especially the fingers, makes taking usable comparison photographs a problem. Special care must be taken to flatten or smooth out the fingers to achieve usable results. Experiments in the lab investigated placing the gloves between two panes of glass, but this created as many problems as it solved. The irregular shape of the gloves formed confusing folds and creases in the latex. Also, the contact of the glass on the powdered surfaces caused some smearing and loss of detail in the developed fingerprints, making this technique unacceptable. Good results were achieved by cutting the gloves apart with scissors, and spreading each finger flat, but this destroyed the gloves in the process.
The best results were achieved using special tools developed for this experiment. Scraps of transparent laminating material (used to make IDs in the crime lab) were cut in the shape of long fingers, between one-half and three-quarters of an inch wide, rounded at the end. These strips could be slid inside the gloves, into the fingers, flattening without distortion. A variety of plastic “fingers” were made to fit the different sizes and fingers of the latex gloves. A palm-shaped insert was also made, flattening out the palm and wrist of the glove. With these tools, acceptable photographs for comparison were made with no difficulty.
Using conventional techniques, latent fingerprints can be successfully developed on latex gloves. Time can be an important factor; some of the clearest prints can be developed using only fluorescent powder shortly after the gloves are removed. The nature of these gloves, and of their removal, makes them an excellent source of clear, identifiable fingerprints. Special care must be taken in photographing this evidence, as the irregular shape can mean unusable comparison photographs for the latent print examiner.